Hybrid vehicles may conserve fuel and reduce greenhouse gases by utilizing an electric motor to provide propulsive effort. Such attributes may be widely known, but a hybrid vehicle may also offer performance advantages. For example, torque of an electric machine may be combined with torque of an internal combustion engine to improve powertrain output and vehicle acceleration. Torques from the electric machine and from the internal combustion engine may be input to a transmission or combined by the transmission and supplied to vehicle wheels. If the internal combustion engine and electric machine provide torque sufficient to cause the vehicle's wheels to slip, the vehicle may not accelerate as fast as desired. Further, the amount of torque that it takes to produce wheel slip may vary based on road surface, tires, and ambient climate conditions. Conversely, if a vehicle driver is requesting a higher rate of vehicle acceleration and torque delivered to the wheels is less than what is needed to meet the higher rate of vehicle acceleration, then the vehicle may under perform. As such, it may be desirable to provide a way of launching a vehicle that provides a desired level of vehicle acceleration without wasting energy spinning wheels.
The inventors herein have recognized the above-mentioned issues and have developed a vehicle operating method, comprising: adjusting speed of a torque converter impeller from a first speed to a second speed in response to contemporaneously applying a brake pedal and an accelerator pedal.
By adjusting a speed of a torque converter impeller before launch of a vehicle in response to brake contemporaneously applied brake and accelerator pedals, it may be possible to improve launch of a hybrid vehicle. In particular, torque converter impeller speed may be adjusted to a stall speed of a torque convertor, or alternatively, to a speed where combined engine torque and electric machine torque is a maximum, before the vehicle is launched so that a time it takes to deliver powertrain torque to wheels may be shortened. Further, engine speed may be adjusted before launch so that engine speed is at a speed where engine torque may be maximized. As such, larger amounts of powertrain torque may be delivered to wheels sooner to improve vehicle acceleration. If wheel slip is experienced during vehicle launch, an electric machine may convert a portion of engine output torque to electrical power, thereby reducing an amount of power lost to wheel slip. Conversely, if engine torque is insufficient to generate wheel slip, the electrical machine may increase wheel torque so that wheel slip may be approached and so that vehicle acceleration enhanced.
The present description may provide several advantages. Specifically, the approach may improve vehicle acceleration during a high performance vehicle launch (e.g., acceleration from vehicle speed of zero until torque converter impeller speed is within a threshold speed of torque converter turbine speed). In addition, the approach may improve vehicle efficiency during a high performance vehicle launch. Further, the approach may provide an optimal amount of wheel slip.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.